Exercise Intolerance in Renal Failure (EIRF)

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Patients with chronic kidney disease have profound exercise intolerance which contributes to an increased risk of cardiovascular disease. The investigators have found that chronic kidney disease patients have an exaggerated increase in blood pressure during certain forms of exercise that could certainly contribute to exercise dysfunction as well as cardiovascular risk. The investigators will test the mechanisms underlying this exaggerated blood pressure response, as well as the potential benefits of short-term tetrahydrobiopterin (BH4) with folic acid on both exercise dysfunction and cardiovascular risk factors in chronic kidney disease. The investigators will test whether short-term treatment with tetrahydrobiopterin (BH4), a cofactor for nitric oxide, together with folic acid improves inflammation, vascular health, and adrenaline levels, both at rest and during exercise in chronic kidney disease.

The augmentation index (AIx) is a measure of systemic arterial stiffness, and is defined as the ratio of augmentation (Δ P) to central pulse pressure and expressed as percent. AIx = (ΔP/PP) x 100, where P = pressure and PP = Pulse Pressure. The mean AIx for each group was estimated as an average and expressed as a change from baseline to 12 weeks.

The augmentation index (AIx) is a measure of systemic arterial stiffness, and is defined as the ratio of augmented aortic pressure (Δ P) to central pulse pressure expressed as a percent. AIx = (ΔP/PP) x 100, where P = pressure and PP = Pulse Pressure. Because heart rate (HR) affects AIx, AIx was corrected to a HR of 75 beats per minute (bpm) as follows: HR-corrected AIx = -0.39 x (75 - HR) + AIx. The mean AIx for each group was estimated as an average and expressed as a change from baseline to 12 weeks.

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1. CKD Stages I, II, and III will be defined as reduction in estimated glomerular filtration rate (eGFR) to 30-59 cc/minute as calculated by the Modification of Diet in Renal Disease (MDRD) equation, or an eGFR>60 cc/minute with proteinuria greater than 500 mg/g of Creatinine or 500 mg per 24 hours.

willing and able to cooperate with the protocol

CKD patients must have stable renal function (no greater than a 20% reduction in eGFR over the prior 3 months)

controls will be matched for age, gender, race, and hypertensive status.